Writing or decorating ceramic surfaces, particularly on zirconia ceramics or oxide ceramics is not easy due to complexities of thermal glazing processes. In such thermal glazing processes, finer details of an image are not normally reproduced on ceramic surfaces. Writing on glass can be accomplished through acid (hydrofluoric) etching. Ceramics are typically decorated through screen printing or hand painting of various features. China and coffee mugs are examples of these technologies. The features imprinted on these objects are then fired at high temperatures to make them permanent and this process is called enameling. There exists a need for reversibly transferring images onto ceramic surfaces.
The present invention is not only capable of finer writing or decorating on the surface of the ceramics, it is also compatible with digital transfer of electronically captured images. The digitally captured images can be imprinted on the ceramic surfaces through use of laser systems. The reversible nature of this image transfer process is one of the most important features of the invention. The erasure of the laser written images can be accomplished in a simple and cost effective manner.
The present invention is a method of imaging a ceramic surface. It includes providing a ceramic having a surface with a contrast, the ceramic consisting essentially of zirconium oxide and a dopant selected from the group of rare earth oxides such as cerium oxide and oxides of calcium, magnesium, yttrium and scandium wherein the ceramic has a molar ratio of dopant to zirconium oxide of from about 0.5:99.5 to about 25:75, depending on the dopant species. For yttria as the dopant, the preferred molar range of yttria to zirconia is from about 0.5:99.5 to about 5.0:95.0. The crystal structure of the zirconia doped ceramic is essentially tetragonal in nature. A laser beam is focused on the ceramic surface, the laser beam having a diameter of 5 .mu.m or greater for a time sufficient to change the contrast of the surface and produce an image. The method of the present invention is reversible in that the image can subsequently be erased.
The present invention also includes an image element comprising a ceramic surface having a first contrast, the ceramic surface consisting essentially of zirconium oxide and a dopant selected from the group of rare earth oxides and oxides of calcium, magnesium, yttrium, scandium and cerium wherein the ceramic has a molar ratio of dopant to zirconium oxide of from about 0.5:99.5 to about 25:75, depending on the dopant species. For yttria as the dopant, the preferred molar range of yttria to zirconia is from about 0.5:99.5 to about 5.0:95.0. The crystal structure of the zirconia doped ceramic is essentially tetragonal in nature. The surface is imaged by focusing a laser beam having a diameter 5 .mu.m or greater on the surface for a time sufficient to change the first contrast. The image on the surface can be erased either through thermal heating or through CO.sub.2 laser assisted heating.
In the present invention, the image quality that can be produced on the ceramic surface is of a much finer quality because grain size of the writing media can be made very small. In addition, the images can be electronically captured and digitally transferred to the media through lasers and the spot size of the lasers can be varied using appropriate optics. Other important advantages of this invention include faster image transference, image erasure, elimination of pretreatments and posttreatments such as thermal treatments of the written surfaces, and no use of chemicals or corrosive acids.